The present invention relates to a cross-connect system for asynchronous transfer mode (ATM) communication and, particularly, to a cross-connect system having a broadcast function.
In order to transmit or transfer voice, data and video information through a communication network, a channel mode of operation and a packet mode of operation are usually employed. In the channel mode operation, time-division multiplexing is employed by periodically arranging time slots so that a call occupies a channel of a constant rate regardless of existence of information. Therefore, the transfer rate is fixed by a particular network facility and degradation of usage efficiency of network resources is unavoidable. These problems are important when transfer rate required is unknown as in case of high rate, wide band communication network, particularly, a wide band ISDN (Integrated Services Digital Network). Therefore, a transfer mode which is not affected by transfer rate is required. On the other hand, in the packet mode, a packet multiplexer using header information is employed in which a packet is transferred upon occurrence of information. Therefore, it is possible to accommodate to any transfer rate. However, in the packet mode, complicated protocols are necessary and software processing for executing these protocols limits the improvement of transfer rate. This becomes a constraint when video information is to be transferred on a real time basis.
In order to solve the problems inherent to the channel mode and packet mode, ATM transmission has been proposed, recently, as the transfer mode and a reduction thereof toward realization is still being developed. The ATM transmission is a technique in which multi-media information is transferred and exchanged after being divided into blocks, referred to as cells, each having a small fixed length and including a header and an information region (header 5 bytes or 40 bits long and information region 48 bytes or 384 bits long in CCITT recommendation I.150 and I.361). ATM, which employs cell multiplexing using header information, can change transfer rate dynamically with a single high speed link of, for example, 156 M bps. Further in ATM transmission, by providing a self-routing switch for allocating a cell according to its header information, the processor does not have any direct contribution in a switch control processing. Therefore, the ATM can transfer multi-media information containing voice and video information which is to be transmitted in real time at a high rate.
When a high speed, wide band communication network is to be constructed using ATM capable of performing high rate transfer of multi-media information while efficiently using network resources, a broadcast function is required, particularly for the application of video information. Communication stations or nodes comprising this communication network are equipped with self-routing switches as cross-connect switches for routing cells to respective destination stations. Conventional self-routing switches proposed are of various types such as the BANYAN type and output buffer type (cf. H. Suzuki, et al., "Output-buffer Switch Architecture for Asynchronous Transfer Mode", IEEE ICC 89, pp. 99-103, June 1989). Therefore, a circuit providing a broadcast function which is adaptable to any type of self-routing switch provided in any node is required.